1. Field of the Invention
The present invention relates to a display apparatus, and more particularly, to a display apparatus in a camera having rotating elements for indicating photographic information.
2. Description of the Related Art
Conventional analog-type clocks have rotating hands that point to numbers on a scale to indicate time. Cameras have recently been manufactured which have a similar type of display device. For example, Japanese Patent Application 4-137225 teaches a display device, in a camera, having rotating pointers to indicate photographic information. The rotating pointers in the camera function similar to the rotating hands in an analog clock. In order to indicate information, such as a frame number or a stop value, pointers in the display device of the camera rotate above pointer scales containing the photographic information. The frame numbers or stop values are displayed on a circular-type scale. A pointer rotates above the scale and points to the correct information. A conventional camera also has a rotary-type setting dial for setting photographic information, such as shutter speed, stop values, and exposure correction values. The display device in the camera displays, using rotating pointers, the photographic information set by the dial.
The problem with this type of camera, however, is that the direction of rotation of the rotary-type setting dial is not always the same as the direction of rotation of the pointers in the display device. A pointer rotating counterclockwise and a dial rotating clockwise will most likely confuse a user of the camera, and make it more difficult to operate the camera.
In conventional analog-type clocks, stepping motors are used to drive the rotation of the hands. The stepping motors are small in size, highly reliable, and produced in large quantities at low cost. It is, therefore, desirable to use stepping motors to drive the rotating pointers in display devices of cameras. However, these conventional analog-clock stepping motors only rotate in one direction. The rotary-type setting dials in cameras can rotate in two directions, i.e., clockwise and counterclockwise. While it is desirable to use the small, reliable, less expensive stepping motors, they cannot rotate pointers in the same direction as the dial rotates. For example, when the dial is rotated in the counterclockwise direction, a clock stepping motor for rotating the pointer rotates the pointer in the clockwise direction. If one were to use a stepping motor to rotate a pointer in a camera, correct information could only be set while rotating the dial clockwise.
Furthermore, clocks do not automatically recognize the present position of its hands. A user is responsible for observing the position of the hands, and making appropriate adjustments upon the detection of a deviation from the correct time. In cameras, however, it is desirable for the camera to automatically recognize the present position of the pointers and to automatically correct for any discrepancies. Such discrepancies may occur, for example, by an external blow of force to the camera, causing the pointers to jump.
Drive mechanisms in clocks do not include detectors that recognize and correct the hand position. This is because such drive mechanisms would increase the cost, weight and size of the clocks. If a position detector switch, for example, were to be arranged in the clock to detect the position of the hands, the load on the drive device for the hands would increase, thereby decreasing the output of the stepping motor. It is difficult to drive the pointers with a weak output from the stepping motor. In order to increase the output, the stepping motor size would increase, the display device would thus become oversized, and its production cost would increase. Such a large and expensive drive motor, for recognizing and correcting pointer positions, is not desirable in a camera.
Instead of using such oversized and expensive drive mechanisms to recognize and correct pointer positions, display devices in cameras typically use stop elements. A stop is arranged at a prescribed position on a pointer scale to limit the rotation of a pointer. A standard position of the pointer is set to be the position of the pointer when it comes in contact with the stop. Then the pointer is driven to rotate from the standard position, and the amount of rotation from the standard position is detected and stored. Due to the stop, however, the pointer cannot continuously rotate in the same direction. A drive motor capable of both clockwise and counterclockwise rotation must be used to drive the rotation of the pointer. The small, reliable and less expensive stepping motor cannot, therefore, be used to drive the pointer.
Moreover, cameras having small display devices exist. In such a small display device, a small rotating pointer display unit is arranged within a large rotating pointer display unit to conserve space. However, sometimes the pointer in the large display unit overlaps the small display unit. This occurs when the pointer in the large display unit points to information near the small display unit. When this happens, it is difficult to set information in the small display unit because a user cannot see the small display unit.